Two piece axle shaft

ABSTRACT

An axle shaft for a differential assembly. The axle shaft includes a shaft structure and a flange structure. The shaft structure has a coupling portion with an engagement surface. The flange structure is formed in a fine blanking operation and has a mounting aperture with a contact surface. The mounting aperture is sized to receive the coupling portion such that the engagement surface and the contact surface are engaged to one another so as to facilitate transmission of rotary power therebetween. The shaft structure and the flange structure are fixedly secured to one another to facilitate the transmission of rotary power therebetween.

FIELD OF THE INVENTION

[0001] The present invention generally relates axle assemblies and moreparticularly to an axle assembly having a two piece axle shaft.

BACKGROUND OF THE INVENTION

[0002] Many motor vehicles employ driveline systems wherein rotary poweris distributed by a differential to a pair of axle shafts. Typically,axle shafts include a flange that is configured to be mated to a wheel,and a shaft, which couples the flange to the differential. The axleshafts known in the art are typically formed, at least partially, by acombination of forging and machining wherein a single steel billet isshaped to the general configuration of an axle by hot forging and coldextrusion. The final finished form is then produced by a series ofsecondary machining operation. Construction of axle shafts in thismanner is known to have several drawbacks.

[0003] One such drawback concerns the overall cost of the axle shaft. Asmentioned above, the axle shaft is initially formed in a forgingoperation so as to provide the axle shaft with a predetermined grainstructure. Forging, however, is a relatively expensive process that istypically incapable of net forming axle shafts and other automotivecomponents. Furthermore, several secondary operations, such asstraightening, are often necessary prior to the finish machining of theforged axle shaft. The finish machining of an axle shaft usually entailsseveral turning operations, several drilling operations, a hobbing orbroaching operation and in most cases, a follow-up heat treatingoperation. As a result of the cost of the capital equipment, perishabletooling and labor associated with these operations, it is relativelycommon for the finish machining costs to be more than twice the cost ofthe axle shaft forging.

[0004] Another drawback concerns the weight of the finished axle shaft.As a forging operation is employed to initially form the axle shaft froma steel billet, the axle shaft is formed with a solid shaft between theends that will ultimately mate to the vehicle wheel and the vehicledifferential. Often times, however, the strength that is provided by thesolid shaft far exceeds that which is necessary and as such, theadditional mass of the solid shaft is undesirable. Removal of thisadditional mass, however, is typically not practical due to the costsassociated with yet another machining operation and/or the impact onother areas of the axle shaft. Assuming, for example, that a drillingoperation could be employed to hollow out the shaft, its costs wouldlikely be prohibitive and there would be some concerns that the holeformed would negatively impact portions of the axle shaft, such as theend portion that couples to the differential.

[0005] Accordingly, there remains a need in the art for an improved axleshaft that is more easily manufactured and lighter in weight thanconventionally forged axle shafts.

SUMMARY OF THE INVENTION

[0006] In one preferred form, the present invention provides an axleshaft for a differential assembly. The axle shaft includes a shaftstructure and a flange structure. The shaft structure has a couplingportion with an engagement surface and the flange structure has amounting aperture with a contact surface. The mounting aperture is sizedto receive the coupling portion to permit the engagement surface and thecontact surface to be engaged to one another so as to facilitatetransmission of rotary power therebetween. In one embodiment, aninterference fit, such as a press fit or a shrink fit, is employed tofix the coupling portion to the mounting aperture and a laser weld isemployed to ensure that the shaft and flange structures remain fixedlysecured to one another. In another embodiment, the laser weld bothsecures the shaft and flange structures to one another as well asfacilitates the transmission of drive torque therebetween.

[0007] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiment of the invention,are intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Additional advantages and features of the present invention willbecome apparent from the subsequent description and the appended claims,taken in conjunction with the accompanying drawings, wherein:

[0009]FIG. 1 is a schematic illustration of a motor vehicle constructedin accordance with the teachings of the present invention;

[0010]FIG. 2 is a cut-away perspective view of a portion of the motorvehicle of FIG. 1, illustrating the rear axle in greater detail;

[0011]FIG. 3 is a section view of a portion of the rear axle illustratedin FIG. 2;

[0012]FIG. 4 is an exploded perspective view of a portion of the rearaxle, illustrating the axle shaft in greater detail;

[0013]FIG. 5 is a partially broken-out side view of the axle shaft;

[0014]FIG. 6 is an partial section view of a vehicle having an axleshaft assembly constructed in accordance with an alternate embodiment ofthe present invention;

[0015]FIG. 7 is a partially broken-out side view of a portion of theaxle shaft assembly of FIG. 6 illustrating the axle shaft in greaterdetail;

[0016]FIG. 7A is an enlarged sectional view of a portion of an axleshaft assembly similar to that of FIG. 7 but illustrating the use ofprojection welds to couple the flange and shaft structures; and

[0017]FIG. 8 is a view similar to that of FIG. 7, but illustrating theaxle shaft as being formed from a tubular blank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] With reference to FIG. 1 of the drawings, a vehicle having adifferential assembly that is constructed in accordance with theteachings of the present invention is generally indicated by referencenumeral 10. The vehicle 10 includes a driveline 12 drivable via aconnection to a power train 14. The power train 14 includes an engine 16and a transmission 18. The driveline 12 includes a drive shaft 20, arear axle 22 and a plurality of wheels 24. The engine 16 is mounted inan in-line or longitudinal orientation along the axis of the vehicle 10and its output is selectively coupled via a conventional clutch to theinput of the transmission 18 to transmit rotary power (i.e., drivetorque) therebetween. The input of the transmission 18 is commonlyaligned with the output of the engine 16 for rotation about a rotaryaxis. The transmission 18 also includes an output and a gear reductionunit. The gear reduction unit is operable for coupling the transmissioninput to the transmission output at a predetermined gear speed ratio.The drive shaft 20 is coupled for rotation with the output of thetransmission 18. Drive torque is transmitted through the drive shaft 20to the rear axle 22 where it is selectively apportion in a predeterminedmanner to the left and right rear wheels 24 a and 24 b, respectively.

[0019] With additional reference to FIGS. 2 and 3, the rear axle 22 isshown to include a differential assembly 30, a left axle shaft assembly32 and a right axle shaft assembly 34. The differential assembly 30includes a housing 40, a differential unit 42 and an input shaftassembly 44. The housing 40 supports the differential unit 42 forrotation about a first axis 46 and further supports the input shaftassembly 44 for rotation about a second axis 48 that is perpendicular tothe first axis 46.

[0020] The housing 40 is initially formed in a suitable casting processand thereafter machined as required. The housing includes a wall member50 that defines a central cavity 52 having a left axle aperture 54, aright axle aperture 56, and an input shaft aperture 58.

[0021] The differential unit 42 is disposed within the central cavity 52of the housing 40 and includes a case 70, a ring gear 72 that is fixedfor rotation with the case 70, and a gearset 74 that is disposed withinthe case 70. The gearset 74 includes first and second side gears 82 and86 and a plurality of differential pinions 88, which are rotatablysupported on pinion shafts 90 that are mounted to the case 70. The case70 includes a pair of trunnions 92 and 96 and a gear cavity 98. A pairof bearing assemblies 102 and 106 are shown to support the trunnions 92and 96, respectively, for rotation about the first axis 46. The left andright axle assemblies 32 and 34 extend through the left and right axleapertures 54 and 56, respectively, where they are coupled for rotationabout the first axis 46 with the first and second side gears 82 and 86,respectively. The case 70 is operable for supporting the plurality ofdifferential pinions 88 for rotation within the gear cavity 98 about oneor more axes that are perpendicular to the first axis 46. The first andsecond side gears 82 and 86 each include a plurality of teeth 108 whichmeshingly engage teeth 110 that are formed on the differential pinions88.

[0022] The input shaft assembly 44 extends through the input shaftaperture 58 where it is supported in the housing 40 for rotation aboutthe second axis 48. The input shaft assembly 44 includes an input shaft120, a pinion gear 122 having a plurality of pinion teeth 124 thatmeshingly engage the teeth 126 that are formed on the ring gear 72, anda pair of bearing assemblies 128 and 130 which cooperate with thehousing 40 to rotatably support the input shaft 120. The input shaftassembly 44 is coupled for rotation with the drive shaft 20 and isoperable for transmitting drive torque to the differential unit 42. Morespecifically, drive torque received the input shaft 120 is transmittedby the pinion teeth 124 to the teeth 126 of the ring gear 72 such thatdrive torque is distributed through the differential pinions 88 to thefirst and second side gears 82 and 86.

[0023] As the left and right axle shaft assemblies 32 and 34 areidentical in their construction and operation, only the left axle shaftassembly 32 will be described in detail. Similar or correspondingelements of the right axle shaft assembly 34 are identified by the samereference numerals as are used to describe the left axle shaft assembly32. The left axle shaft assembly 32 includes an axle tube 150 that isfixed to the left axle aperture 54 and an axle shaft 152 that issupported by a bearing 154 for rotation in the axle tube 150 about thefirst axis 46. As those skilled in the art will appreciate, the leftaxle shaft assembly 32 is illustrated to be of a semi-floating designwherein the axle shaft 152 supports a portion of the weight of thevehicle 10.

[0024] With additional reference to FIGS. 4 and 5, the axle shaft 152 isshown to include a shaft structure 160 and a flange structure 162. Theshaft structure 160 is shown to include a body portion 170, a bearingsupport portion 172, an input portion 174, and a coupling portion 176.The body portion 170 is generally uniform in its cross-section and iscoupled at opposite ends to the bearing support portion 172 and theinput portion 174. The bearing support portion 172 includes a bearingsurface 180 that is sized to engage in a press-fit manner the innerbearing race of the bearing 154 and in the particular embodimentillustrated, has an outer diameter that is generally larger than that ofthe body portion 170. The coupling portion 176 is fixedly coupled to theopposite end of the bearing support portion 172 and is configured tocouple the shaft structure 160 to the flange structure 162. The couplingportion 176 includes a head portion 182 having an abutting flange 184,and an engagement surface 186. In the example provided, the head portionis includes a plurality of lobed teeth, but may alternatively be formedwith any other geometric shape. The head portion 182 terminates at theabutting flange 184. The abutting flange 184 extends circumferentiallyaround the coupling portion 176 and radially outwardly of the engagementsurface 186. The engagement surface 186 may have a circular shape but ispreferably non-circular in shape with an outer diameter or dimensionthat is generally larger than the diameter of the bearing surface 180.In the particular embodiment illustrated, the engagement surface 186includes a plurality of circumferentially spaced spline teeth 188 whichwill be discussed in greater detail, below. Those skilled in the artwill understand from the description below, however, that anyappropriate geometric shape may be substituted for the spline teeth 188,including lobes, or even smooth, particularly in the case of a shrinkfit or welded construction.

[0025] The input portion 174 is shown to include an input spline 190 anda lock slot 192 and in the particular embodiment illustrated, is neckeddown somewhat from the body portion 170. The input spline 190 includes aplurality of spline teeth 194 that are configured to meshingly engage aplurality of spline teeth 196 that are formed in the first side gear 82.Meshing engagement of the spline teeth 194 and 196 facilitates thetransmission of rotary power from the differential unit 42 to the shaftstructure 160. The lock slot 192 is an annular groove that is formedinto the perimeter of the input portion 174. The input spline 190 and anannular wall member abut the opposite sides of the lock slot 192. Thelock slot 192 is sized to receive a conventional C-lock clip (not shown)which is employed to couple the input portion 174 to the first side gear82 in a manner that is well known to those skilled in the art.

[0026] In the particular embodiment illustrated, the shaft structure 160is formed from a hollow, tubular blank which substantially reduces theoverall weight of the axle shaft 152 as compared with a conventionallyconstructed solid axle shaft. In a presently preferred embodiment, awelded seam tubular material having an elongated grain structure isemployed to form the tubular blank. The tubular blank is initiallyrotary swaged and/or orbitally forged over a mandrel (not shown) topre-form the coupling portion 176, the input portion 174 and the bearingsurface 180, as well as to close off the hollow central cavity in anarea proximate the input portion 174 to inhibit fluids from flowingthrough the axle shaft 152. Additional operations, such as roll forming,turning and/or grinding, are employed to net form or near-net formportions of the shaft structure 160. For example, features such as theinput spline 190, the spline teeth 188 of the engagement surface 186,the lobes 182 a of the head portion 182, and the abutting flange 184 arenet-formed in a roll forming operation. The lock slot 192 is near-netformed in a roll forming operation and thereafter finished machined in aturning operation. The bearing surface 180 is near-net formed in a rollforming operation and is finished in an appropriate machining operation,such as grinding, after the input spline 190, the spline teeth 188 andthe bearing surface 180 have been appropriately heat treated, as byinduction hardening.

[0027] The flange structure 162 is a one-piece annular plate, having awheel mounting portion 200 and a center hub 202. The wheel mountingportion 200 includes a generally flat abutting face 210, which isconfigured to abut an associated one of the wheels 24, and a pluralityof cylindrically shaped, circumferentially spaced wheel stud mountingapertures 212 that extend through the wheel mounting portion 200 on anaxis that is perpendicular to the abutting face 210. Each wheel studmounting aperture 212 is sized to engage in a press-fit manner aconventional wheel stud 216 having a head 218 and a threaded portion220. The head 218 of the wheel stud 216 abuts a side 222 of the wheelmounting portion 200 opposite the abutting face 210 and the threadedportion 220, which is configured to threadably engage a conventional lugnut (not shown), extends outwardly from the abutting face 210.

[0028] The center hub 202 includes a mounting aperture 230 that is alsoarranged perpendicular to the abutting face 210. The mounting aperture230 includes an annular lip 232 and a contact surface 234. The contactsurface 234 is configured to engage the engagement surface 186 of thecoupling portion 176 in a manner that facilitates the transmission ofrotary power therebetween. In the example provided, a plurality ofspline apertures 238 are formed into the perimeter of the mountingaperture 230. Additionally, the mounting aperture 230 is sized toreceive the coupling portion 176 in a press-fit manner. The annular lip232 abuts the abutting flange 184 and as such, cooperates with theabutting flange 184 to permit the flange structure 162 to be positionedon the shaft structure 160 at a predetermined location.

[0029] Also in the example provided, the center hub 202 is elongatedsomewhat along the axis of the mounting aperture 230 so as to increasethe robustness of the interconnection between the shaft structure 160and the flange structure 162. In this regard, the center hub 202includes a secondary mounting aperture 240 having a secondary contactsurface 242 that engages the outer surface 244 of the head portion 182to permit the transmission of rotary power therebetween. Accordingly,the secondary mounting aperture 240 is sized to receive at least aportion of the head portion 182 and as such, includes a plurality oflobes 240 a that are configured to meshingly engage the lobes 182 a ofthe head portion 182. As with the connection between the engagementsurface 186 and the contact surface 234, an interference fit, such as apress fit or a shrink fit, is preferably employed to secure thesecondary contact surface 242 to the outer surface 244 of the headportion 182. As those skilled in the art will understand, a second weld250 may additionally or alternatively be employed to fixedly couple thehead portion 182 to the center hub 202.

[0030] Advantageously, the head portion 182 is sized so as not to permitthe shaft structure 160 to slide completely through the flange structure162. Construction in this manner ensures that the flange structure 162will remain coupled to the shaft structure 160 even in situations wherethe coupling means (i.e., the interference fit(s) and/or laser weld)that fixes these components together has failed.

[0031] The flange structure 162 is preferably entirely formed in a fineblanking operation. In a presently preferred embodiment, the materialfrom which the flange structure 162 is formed is a sheet or flat stockmaterial that has been processed in a rolling operation to elongate thegrain structure in a predetermined direction. As those skilled in theart will understand, fine blanking is a controlled shearing process inwhich a tightly clamped workpiece is forced through a die opening toproduce accurate workpieces with a fine finish and relatively straightedges. However, those skilled in the art will understand thatalternative and/or additional forming and/or machining operations mayalso be employed to form the flange structure 162. For example, theflange structure 162 may initially be formed in a stamping operationwith an undersized mounting aperture 230 and thereafter processedthrough a secondary operation, such as a broaching operation, to finishthe mounting aperture 230.

[0032] With the shaft structure 160 and the flange structure 162initially formed in the manner described above, they are thereafterassembled such that the coupling portion 176 is engaged to the mountingaperture 230. The flange structure 162 is abutted against the couplingportion 176 such that the annular lip 232 abuts the abutting flange 184.The shaft structure 160 and the flange structure 162 are thereafterlaser welded so as to ensure that they remain fixedly coupled to oneanother. In the example provided, the engagement and contact surfaces186 and 234 are configured to transmit rotary power between the shaftstructure 160 and the flange structure 162. In this regard, it ispresently preferred that an interference fit, such as a press fit or ashrink fit, be employed to fixedly couple the shaft structure 160 andthe flange structure 162 and that the laser weld 250 not serve as theprimary means for transferring rotary power between the shaft structure160 and the flange structure 162. As such, the laser weld 250 may besized in a relatively small manner so as to minimize the amount of heatthat is delivered to the shaft structure 160 and the flange structure162 when it is being formed. Those skilled in the art will understand,however, that the coupling of the shaft structure 160 and the flangestructure 162 may be accomplished somewhat differently. For example, aninterference fit alone may be employed to fixedly couple the shaft andflange structures 160 and 162 and transmit rotary power therebetween. Asanother example, the laser weld alone may be employed to both fixedlycouple the shaft and flange structures 160 and 162 and transmit rotarypower therebetween.

[0033] While the axle shafts of the present invention have beendescribed thus far with reference to a semi-floating axle assembly,those skilled in the art will appreciate that the present invention, inits broader aspects, may be constructed somewhat differently. Forexample, the axle shafts of the present invention may be similarlyincorporated into a full-floating axle as illustrated in FIGS. 6 and 7.As illustrated, an axle shaft assembly 300 is shown in association withan axle assembly 302 and a wheel 304. The axle assembly 302 includes ahousing 306 with a pair of outwardly extending hollow hubs 308 (only oneof which is shown). The housing 306 is otherwise similar to housing 40discussed above. A pair of bearings 310 are disposed between each hub308 and an associated wheel 304 and operatively support the wheel 304for rotation on the hub 308. Each of the axle shaft assemblies 300includes an axle shaft 320 having a shaft structure 322 and a flangestructure 324. The shaft structure 322 is shown to extend through thehollow cavity 326 in the hub 308 and is coupled to a differential unit(not shown) that is similar in its construction and operation to thedifferential unit 42 described above. The flange structure 324 iscoupled to the wheel 304 and cooperates with the shaft structure 322 totransmit drive torque from the differential to the wheel. As thoseskilled in the art will appreciate, the axle shaft assembly 300 isillustrated to be of a full-floating design, wherein the axle shaft 320drives the wheel 304 but does not hold the wheel 304 or carry the weightof the vehicle.

[0034] Generally, the axle shaft 320 is similar to the axle shaft 152,being simplified somewhat in view of the fact that a bearing surfaceneed not be formed on the shaft structure 322. Accordingly, the shaftstructure 322 includes a body portion 170′, an input portion 174′, and acoupling portion 176′, which are substantially similar in theirconstruction to the body portion 170, input portion 174 and couplingportion 176, respectively, of the axle shaft 152 described above. Assuch, the shaft structure 322 will not be discussed in detail other thanto note that the coupling portion 176′ includes an engagement surface186′ and a secondary engagement surface 244′, both of which arepreferably non-circular in shape. In the particular embodimentillustrated, the engagement surface 186′ includes a plurality ofcircumferentially spaced spline teeth 188′ and the secondary engagementsurface 244′ includes a plurality of lobes 182 a′, both of which will bediscussed in greater detail, below. Those skilled in the art willunderstand from the description below, however, that any appropriategeometric shape may be substituted for the spline teeth 188′ and thelobes 182 a′ or that these interfaces may be cylindrical. Those skilledin the art will also readily understand that the axle shaft 320 may beformed from a solid billet as shown in FIG. 7, or may be formed from ahollow tube 330, as shown in FIG. 8.

[0035] Referring back to FIGS. 6 and 7, the flange structure 324 isillustrated to be similar to the flange structure 162, in that it isalso a one-piece annular plate which is preferably formed in a fineblanking operation. The flange structure 324 includes a wheel mountingportion 200′ and a center hub 202′. The wheel mounting portion 200′includes a generally flat abutting face 210′, which is configured toabut an associated one of the wheels 304, and a plurality ofcylindrically shaped, circumferentially spaced wheel stud receivingapertures 216′ that extend through the wheel mounting portion 200′ on anaxis that is perpendicular to the abutting face 210′ and which are sizedto receive the threaded portion 334 of a conventional wheel stud 336. Anut 338 is threadably engaged to the threaded portion 334 and generatesa clamping force that fixes the flange structure 324 to the wheel 304.

[0036] The center hub 202′ includes a mounting aperture 230′ that isarranged perpendicular to the abutting face 210′ and which includes acontact surface 234′, as well as a secondary mounting aperture 240′having a secondary contact surface 242′. The contact surface 234′ isconfigured to engage the engagement surface 186′ of the coupling portion176′ in a manner that facilitates the transmission of rotary powertherebetween. In the example provided, a plurality of spline apertures238′ are formed into the perimeter of the mounting aperture 230′. Alsoin the example provided, the secondary contact surface 242′ includes aplurality of lobes 240 a′ that are configured to matingly engage lobes182 a′ formed into the secondary engagement surface 244′. As with thepreviously described embodiment, the mounting aperture 230′ and thesecondary mounting aperture 240′ are preferably sized such that theengagement surface 186′ and the contact surface 234′, as well as thesecondary engagement surface 244′ and the secondary contact surface242′, are fixedly coupled with an interference fit. One or more laserwelds 250′ may additionally or alternatively be employed to fix theshaft structure 322 and the flange structure 324 to one another. Withreference to FIG. 7A, a plurality of projections 350 are alternativelyformed onto one of the contact surface 234′ and the secondary contactsurface 242′. The projections 350 facilitate a projection weldingoperation that fixedly couples the head portion 182′ to the flangestructure 324.

[0037] With the shaft structure 322 and the flange structure 324 formedin the manner described above, they are thereafter assembled such thatthe coupling portion 176′ is engaged to the mounting aperture 230′. Theshaft structure 322 and the flange structure 324 are thereafter laserwelded so as to ensure that they remain fixedly coupled to one another.As discussed above, however, the engagement surface 186′ and the contactsurface 234′ are preferably configured to transmit rotary power betweenthe shaft structure 322 and the flange structure 324. Accordingly, thelaser weld 250′ need not serve as a significant means for transferringrotary power between the shaft structure 322 and the flange structure324.

[0038] While the invention has been described in the specification andillustrated in the drawings with reference to a preferred embodiment, itwill be understood by those skilled in the art that various changes maybe made and equivalents may be substituted for elements thereof withoutdeparting from the scope of the invention as defined in the claims. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment illustrated by the drawingsand described in the specification as the best mode presentlycontemplated for carrying out this invention, but that the inventionwill include any embodiments falling within the foregoing descriptionand the appended claims.

What is claimed is:
 1. An axle shaft for a differential assembly, theaxle shaft comprising: a shaft structure having a coupling portion withan engagement surface; a fine blanked flange structure having a mountingaperture with a contact surface, the mounting aperture being sized toreceive the coupling portion such that the engagement surface and thecontact surface are engaged to one another so as to facilitatetransmission of rotary power therebetween; and means for coupling theshaft structure and the flange structure.
 2. The axle shaft of claim 1,wherein the shaft structure is formed from a first material and theflange structure is formed from a second material that is different fromthe first material.
 3. The axle shaft of claim 1, wherein the shaftstructure is formed from a generally tubular material.
 4. The axle shaftof claim 3, wherein the tubular material is welded tubing.
 5. The axleshaft of claim 3, wherein at least a portion of the shaft structure isformed in a rotary swaging operation.
 6. The axle shaft of claim 1,wherein the engagement surface has a non-circular shape that isconfigured to matingly engage the contact surface.
 7. The axle shaft ofclaim 6, wherein one of the engagement and contact surfaces includes aplurality of spline teeth for engaging a plurality of spline aperturesformed in the other one of the engagement and contact surfaces.
 8. Theaxle shaft of claim 7, wherein the plurality of spline teeth are formedonto the shaft structure in a roll forming operation.
 9. The axle shaftof claim 1, wherein the coupling means includes at least one laser weld.10. The axle shaft of claim 1, wherein the coupling means includes atleast one projection weld for fixedly coupling the shaft structure andthe flange structure.
 11. The axle shaft of claim 1, wherein thecoupling means includes an interference fit between the engagementsurface and the contact surface.
 12. The axle shaft of claim 1, whereinthe shaft structure includes an input spline that is adapted to matinglyengage a spline aperture formed in a side gear of the differentialassembly.
 13. The axle shaft of claim 1, wherein the coupling portionfurther includes a head portion that is at least partially disposedwithin a secondary mounting aperture formed into the flange structure.14. The axle shaft of claim 13, wherein the head portion has a diameterthat is larger than a diameter of the mounting aperture.
 15. The axleshaft of claim 13, wherein the coupling means includes at least onelaser weld for fixedly coupling the head portion to the flangestructure.
 16. The axle shaft on claim 13, wherein the coupling meansincludes at least on projection weld for fixedly coupling the headportion and the flange structure.
 17. The axle shaft of claim 13,wherein the coupling means includes an interference fit between the headportion and the secondary mounting aperture.
 18. The axle shaft of claim13, wherein the head portion includes a secondary engagement surface andthe secondary mounting aperture has a secondary contact surface, thesecondary engagement surface having a non-circular shape that isconfigured to matingly engage the secondary contact surface.
 19. Theaxle shaft of claim 18, wherein one of the secondary engagement andsecondary contact surfaces includes a plurality of spline teeth forengaging a plurality of spline apertures formed in the other one of thesecondary engagement and secondary contact surfaces.
 20. The axle shaftof claim 19, wherein the plurality of spline teeth are formed onto thehead portion in a roll forming operation.
 21. The axle shaft of claim 1,wherein the flange structure is formed from a sheet material that hasbeen processed in a rolling operation.
 22. The axle shaft of claim 1,wherein the shaft structure further comprises a bearing surface that isadapted to engage in a press-fit manner a race of a bearing.
 23. An axleassembly comprising: an axle housing; a differential assembly disposedwithin and rotatably supported by the axle housing, the differentialassembly operatively receiving a drive torque input and distributing thedrive torque input to a pair of output gears; and a pair of axle shafts,each axle shaft including a shaft structure and a flange structure, theshaft structure having a coupling portion with an engagement surface,the flange structure being at least partially formed in a fine blankingoperation and having a mounting aperture with a contact surface, themounting aperture being sized to receive the coupling portion such thatthe engagement surface and the contact surface are engaged to oneanother so as to facilitate transmission of rotary power therebetween,wherein the shaft structure and the flange structure are fixedly securedto one another.
 24. The axle assembly of claim 23, wherein the shaftstructure is formed from a first material and the flange structure isformed from a second material that is different from the first material.25. The axle assembly of claim 23, wherein the shaft structure is formedfrom a generally tubular material.
 26. The axle assembly of claim 25,wherein the tubular material is welded tubing.
 27. The axle assembly ofclaim 25, wherein at least a portion of the shaft structure is formed ina rotary swaging operation.
 28. The axle assembly of claim 23, whereinthe engagement surface has a non-circular shape that is configured tomatingly engage the contact surface.
 29. The axle assembly of claim 28,wherein one of the engagement and contact surfaces includes a pluralityof spline teeth for engaging a plurality of spline apertures formed inthe other one of the engagement and contact surfaces.
 30. The axleassembly of claim 29, wherein the plurality of spline teeth are formedonto the shaft structure in a roll forming operation.
 31. The axleassembly of claim 29, wherein at least one laser weld is employed tofixedly couple the flange structure and the shaft structure.
 32. Theaxle shaft of claim 23, wherein the coupling means includes at least oneprojection weld for fixedly coupling the shaft structure and the flangestructure.
 33. The axle assembly of claim 23, wherein an interferencefit between the engagement surface and the contact surface is employedto fixedly couple the flange structure and the shaft structure.
 34. Theaxle assembly of claim 23, wherein each of the shaft structures includesan input spline that is configured to matingly engage a spline apertureformed in one of the output gears of the differential assembly.
 35. Theaxle assembly of claim 23, wherein the coupling portion further includesa head portion that is at least partially disposed within a secondarymounting aperture formed into the flange structure.
 36. The axleassembly of claim 35, wherein the head portion has a diameter that islarger than a diameter of the mounting aperture.
 37. The axle assemblyof claim 35, wherein at least one laser weld is employed to fixedlycouple the head portion to the flange structure.
 38. The axle assemblyof claim 35, wherein an interference fit between the head portion andthe secondary mounting aperture is employed to fixedly couple the headportion to the flange structure.
 39. The axle assembly of claim 35,wherein the head portion includes a secondary engagement surface and thesecondary mounting aperture has a secondary contact surface, thesecondary engagement surface having a non-circular shape that isconfigured to matingly engage the secondary contact surface.
 40. Theaxle assembly of claim 39, wherein one of the secondary engagement andsecondary contact surfaces includes a plurality of spline teeth forengaging a plurality of spline apertures formed in the other one of thesecondary engagement and secondary contact surfaces.
 41. The axleassembly of claim 40, wherein the plurality of spline teeth are formedonto the head portion in a roll forming operation.
 42. The axle assemblyof claim 23, wherein the flange structure is formed from a sheetmaterial that has been processed in a rolling operation.
 43. The axleassembly of claim 23, wherein the shaft structure further comprises abearing surface that is adapted to engage in a press-fit manner a raceof a bearing.